Speculation that Jesus Christ might have married is an ancient one and, however often theologians and historians throw cold water over the idea, it will keep cropping up – most notably in recent years as a key element in the plot of Dan Brown's The Da Vinci Code. No one would take that particular novel as gospel, but now a historian from the Harvard Divinity School has come up with what may – just – be the first ever reference to Jesus mentioning a wife.

The fragment of fourth-century Coptic writing on a rectangular piece of faded papyrus no more than eight centimetres by four contains eight lines written in black ink apparently including the words: "Jesus said to them, 'My wife …'" Far from being the start of a music-hall joke, the extract continues: "she will be able to be my disciple," before being cut off.

Karen L King, the Hollis professor of divinity – the oldest endowed academic chair in the US – who made the discovery, told the New York Times: "These words can mean nothing else."

She should know – King is a Coptic scholar and author of books on the heretical Gnostic gospels from which claims about Jesus's marriage originate. Cautious academic that she is, she hasn't leapt off hither and thither in a private plane like Dan Brown's hero, but has shared her discovery with other scholars who believe that the papyrus sliver may be genuine, though its provenance is obscure. It is apparently owned by an anonymous private collector, who bought it in 1997 from a German professor who is now dead – a suitably mysterious touch.

Roger Bagnall, director of New York University's Institute for the Study of the Ancient World, who was shown the fragment, told the paper: "It's hard to construct a scenario that is at all plausible in which someone fakes something like this. The world is not really crawling with crooked papyrologists."

Diarmaid MacCulloch, Oxford professor of the history of the church, says: "If this is genuine, it is fantastically interesting and the first reference to Jesus and wife, but it was almost certainly written in the context of an early debate on the position of women in the church. It certainly doesn't give carte blanche to the likes of Dan Brown and the idiots who think like him."

Even if the reference is authentic, it was still written about as far from Christ's birth as we are from Shakespeare's. Although the Biblical gospels contain metaphorical references to Christ, saying he is a bridegroom, they mean he is married to the church and there is no reference to a real wife. Nevertheless, it is known there was a debate in the early church about whether he could have been married, as part of ongoing arguments over the role of women in the sect. Women had senior positions in the church before being pushed aside: a position they are only just regaining in the Church of England nearly 2,000 years later if they are finally allowed to become bishops.

Apocryphal gospels – the ones church authorities later decided were not authentic enough to include in the Bible – do contain woman-friendly references: ambiguous and cloudy as they often are. The gospel of Thomas, written in the first century, has Jesus siding with his follower Mary Magdalene against St Peter when the apostle demands that she should be sent away. The Gnostic, heretical, gospel of Philip, among documents discovered at Nag Hammadi in Egypt in 1945 – written in Coptic in the fourth century like the current fragment, apparently based on earlier Greek texts – has Christ kissing Mary. And the second-century gospel of St Mary quotes a disciple called Levi telling Peter: "If the Saviour made her worthy, who are you to reject her? Certainly the Saviour knows her very well. That is why he loved her more than us."

MacCulloch explains: "There were far more wacky things in some of the Gnostic gospels than that Jesus might have married, like that he wasn't crucified at all but sat up in heaven giggling at the man who was executed in his place." None of the scattered references to a wife translates to either a sexual relationship, or a marriage ceremony, but it is Mary Magdalene with whom Christ is usually hitched. She is a shadowy figure who is given a place in the Biblical gospels, watching the crucifixion and finding Christ's empty tomb on the morning of Easter Sunday. As the first witness to the Resurrection, the central tenet of Christianity, that makes her technically the first Christian. Her name indicates that she came from Magdala in Galilee.

The idea that she had been a prostitute is a much later one, but that probably gives a frisson to the idea that she was married to Jesus and that therefore there may be a hidden bloodline and living descendants – though if there are, after so many generations we probably all have a little bit of Jesus in us. Heretics such as the medieval Cathars and their modern equivalents, the pseudo-historians and conspiracy theorists – and Dan Brown – have taken up the fantasy.

Mary's other modern image – as a sensually attracted Jesus groupie – probably dates back to the writings of the 19th-century French ex-monk Ernest Renan, from whose writings much of the idea of a mystical, gentle Jesus originates. If she existed – and the Biblical gospels all mention her – she was clearly a follower and maybe a sponsor of Jesus and his disciples on their travels around the Holy Land. Maybe she was actually unable to marry anyone for some medical or other reason.

King gave her findings at a conference of Coptic scholars in Rome on Tuesday, though interestingly – perhaps indicative of how sensitive the subject is in church quarters – the Vatican's newspaper and radio made no mention of her lecture in their coverage of the event.

The professor herself is also being suitably academically cautious. "At least don't say this proves Dan Brown was right," she told the New York Times. Or, as MacCulloch says: "Bloggers beware – it's not what you think."

Stephen Bates is the Guardian's former religious affairs correspondent.

•This article was amended on 19 September 2012. The sentence "Even if the reference is authentic, it was still written at least 100 years after Christ's birth" was changed to "Even if the reference is authentic, it was still written as far away from Christ's birth as we are from Shakespeare's"